High resolution magic angle spinning (MAS) nuclear magnetic resonance (NMR) spectroscopy is a powerful and versatile technique for studying molecular structure and dynamics in solid systems, semi-solid systems, or heterogeneous systems containing mixtures of e.g., solid, semi-solid, liquid, and gaseous phases. Thus MAS NMR is an attractive tool for in-situ investigations of reaction dynamics and intermediates, investigations of properties of active sites in catalysts during catalytic conversion of biogenic molecules in aqueous phase water, and physical/chemical properties and/or phase transitions in materials and material syntheses. However, reusable sample cells that perform well at temperatures greater than about 100° C. and pressures greater than the vapor pressure of aqueous water have not been realized in MAS NMR to date due primarily to technical difficulties associated with sealing heterogeneous fluid samples at high temperature and high pressure conditions that would prevent leakage of fluids while spinning samples at a spinning rate of several kHz or more inside a strong magnetic field. To date, MAS NMR experiments have been performed at pressures of about 150 bar and temperatures up to 80° C. using a zirconia rotor sleeve and plastic components including bushings, O-rings, valves, and valve adaptors detailed, e.g., by Hu et al. in “High-Pressure Magic Angle Spinning Nuclear Magnetic Resonance”, J. Magn. Reson., 212, 378-385 (2011); Hu et al. in “Rotor Design for High Pressure Magic Angle Spinning Nuclear Magnetic Resonance”, J. Magn. Reson., 226, 64-69 (2012); and US Patent Publication No.: 2012/0146636. However, plastic components soften at higher temperatures, rendering previous designs unsuitable at temperatures above 100° C. Accordingly, new rotor designs are needed that provide sealing of heterogeneous fluid samples at high temperature and high pressure conditions and prevent leakage of fluids while spinning samples at spinning rates of several kHz or more inside strong magnetic fields. The present invention addresses these needs.